Seagrass bed habitat is an important biotic community in decline worldwide. Boat damage has long been recognized for its negative impacts on shallow-water seagrass beds, with those along the Florida coast particularly vulnerable in the face of a large human population possessing a large number of boats. Boat scars to seagrass beds recover slowly, resulting in new damage that often outpaces recovery of existing damage. We examined the rate of accumulation of total area composed of boat scars from 1994 to 2005 at Lignumvitae Key Submerged Land Managed Area, an area containing approximately 3400 ha of seagrass beds. We found the total area of damage increased from 1994 to 1997 by an average of 27.1 ha/y and from 1997 to 2005 by an average of 10.8 ha/y. This most recent rate of damage increase represents an additional $1,523,819 annual loss in habitat value using cost figures based on costs from restoration attempts permitted by the Environmental Protection Agency. Severe groundings investigated by law enforcement officers showed increasing trends over time in the average amount and severity of damage. The size of the boat inflicting the damage was more closely related to the severity of damage than to the amount of damage. The most immediate and practical measures for preventing damage include increasing signage to warn boaters to avoid seagrass beds and increasing law enforcement staff. Signage is a relatively low-cost, long-term investment that becomes cost-effective even if only 0.03 ha of seagrass bed damage is averted over the life of the signs. Each patrol staff member added becomes cost-effective even if only 0.42 ha of damage is averted annually. Holding the total area of damage constant for 1 year (new damage = recovery) would represent a benefit–cost ratio of 25.71 if accomplished with only one additional law enforcement officer.

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